1. Field of the Invention
The present invention relates to an exposure apparatus and a method of manufacturing a device using the same.
2. Description of the Related Art
A scanning exposure apparatus which exposes a wafer while scanning a mask and the wafer with respect to an optical system is the current mainstream exposure apparatus for manufacturing a semiconductor device. To improve the resolution, the scanning exposure apparatus must maintain constant the exposure amount (dose) per unit area, at which the wafer is irradiated with light during scanning. To do this, it is of prime importance to appropriately set, for example, the amount of light emitted by a pulsed light source and the interval between light emissions according to the wafer moving velocity.
In the conventional exposure apparatus, a wafer stage has a driving profile formed by a combination of an acceleration interval, settlement interval, constant velocity interval, and deceleration interval. Note that the settlement interval means the interval from completion of stage acceleration until the start of the constant velocity interval, that is, the transition interval until the control error that must be settled to position the stage becomes sufficiently small. A general scanning exposure apparatus performs exposure in the constant velocity interval in which the exposure amount on the wafer can easily be controlled to be constant. This is because in the constant velocity interval, simply maintaining the amount of light from the light source constant makes it possible to maintain the dose constant, thus easily sustaining high dose control accuracy.
The exposure apparatus is required to attain not only a given exposure accuracy and overlay accuracy but also a high productivity. This requirement has conventionally been met by increasing the power of a stage driving unit so that the stage can be driven at a high acceleration and velocity. On the other hand, Japanese Patent Laid-Open No. 2002-373839 proposes an exposure system which performs exposure even in the acceleration interval, settlement interval, and deceleration interval while changing the exposure amount of light from the light source in proportion to the stage velocity, to maintain the dose constant.
Exposure during acceleration/deceleration in the prior art technique poses the following problem. That is, in intervals other than the constant velocity interval, the control error associated with the stage position is relatively large, and the positioning accuracy between the optical system and the stage is relatively low, so the overlay accuracy is relatively low. Also, in the intervals other than the constant velocity interval, the control error associated with the stage velocity is large, so adjustment of the exposure amount with higher accuracy requires controlling the stage in consideration of a stage velocity error. This not only complicates an exposure amount controller but also increases the number of factors which degrade the exposure amount controllability. Furthermore, to perform dose control with high accuracy, it is necessary to change the exposure amount of light from the light source so that it follows a change in stage velocity. However, in the stage acceleration and deceleration intervals, the velocity change rate is relatively high, so the exposure amount controllability degrades.